Tories



June 12, 1928. v -1 ,673,66l

- C. E. BRIGHAM ELECTROMAGNETIC SOUND REPRODUCING APPARATUS Filed Feb. 16, 1925 ET-ATIY: SOUND MEN 3ITZ ATIORNEY CECIL. E. BEIGHAM. INVENTOR.

Patented June 12, 1928.

UNITED ,STATES PATENT OFFICE.

CECIL 15. BRIGHAM, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO BRANDES LABORA- TOEIES, INC., F NEWARK, NEW JERSEY, A CORPORATION OF NEW JERSEY.

ELECTROMAGNETIC SOUND-REPRODUCING APPARATUS.

Application filed February 16, 1926. Serial No. 88.573.

M y invention relates broadly to sound reproducing apparatus and more particularly to the onstruction of a diaphragm for an electromagnetic sound reprodueer.

One of the objects of my invention is to provide a sound reproducing diaphragm for electromagnetic sound reproducers having such properties that more eflicicnt reproduction may be obtained over a greater frequency range than has heretofore been pos sible.

Ai'ioti'uirr object of my invention is to pro vide a construction of electronulgnetic sound reproducing diaphragm having a greater path for magnetic flux through the dianhragm than has: heretofore been possible, at the same time that increased flexibility in the diaphragm construction is obtained and interference between sound waves emanating from the. opposite sides of the diaphragm suhst a at ially eliminated.

Still another object of my invention is to provide a diaphragm ct'instruction for electromagnetic sound reproducers in which a magnetic diaphragm is perforated over seleeted portions of its area and the perforations closed by material substantially inert to eddy currents and having a density less than tlu matcrial of the diaphragm for obtaining great flexibility in the diaphragm structure, while preventing interference between sound waves emanating from opposite sides of the diaphragm.

Other and further objects of my invention will be understood from the specification hereinafter following by reference to the accompanying drawings. in which: I

Figure l is a pla n-view showing the constrm-tion of my improved diaphragm; Fig. 2 is a cross-sectional view through an electromagnetic sound reproducer equipped with the diaphragm of my construction; F g. 3' is an enlarged cross-sectional view through the diaphragm construction of my invention; and Fig. 4 shows a plurality of sound curves illustrating the improved results obtained by the use of the sound reproducing diaphragm of my invention as oonmarerl to diaphragms heretofore availn the art.

The electromagnetic sound reproducers used in he reception of radio broadcast enterta-inment it is extremely difficult to secure natural reproduction of all of the notes of the musical scale throughout the entire range of frequencies. The frequencies at either end of the scale are often sacrificed and the tones distorted or impaired. The sound reproducing diaphragm of my invention is constructed for the efficient reproduction of tone frequencies over a broad frequency range and produces results which are a marked improvement over the results obtained from diaphragm constructions heretofore available. I provide a magnetic diaphragm of increased thickness over the normal thickness of magnetic diaphragms heretofore commonly used for establishing a greater path formagnetic flux from the adjacent elcctromagncts through the diaphragm. The flexibility of a diaphragm of less thickness is obtained by perforating the diaphragm throughout portions of its area and these perforations are then closed for the preventing of interference between sound waves emanating from opposite sides of the, diaphragm. The i'naterlal employed for closing the perforations is an insulating compound which is inert to the etfccts of eddy currents and has a density less than the density of the magnetic material of the diaphragm. phragm of my invention will be more clearly understood by a detailed reference to the drawings, wherein reference character 1 designates the magnetic diaphragm which is perforated as represented at 2 around the central solid porti n 3. It will be observed that the outer periphery 4 is solid while the inner central portion 3 is solid and the magnetic lines of force which are incident upon the diaphragm are concentrated from pole pieces 5 immediately beneath the central solid portion 3 of the sound reproducing diaphragm 1. The perforations 2 fill the area intermediate the solid outer periphery portion 4 and the central portion 3. The perforations are formed in concentric circles and along radial lines. the perforations in one circle alternating with the perforations in the next. adjacent circle.

In Figure 2 an electromagnetic sound. reproducer has been illustrated comprising a c ing 6 which terminates in a. sound con- The construction of the dia veying conduit 7. The interior walls of the casing 6 are screw threaded as represented at 8 permitting a screw threaded carrier 9 to be adjustably positioned therein. The screw threaded carrier 9 carries the electron'iagncts 10 having pole pieces 5. An annular screw threaded member 11 is provided for supporting the diaphragm 1 within the casing 6. A resilient gasket 12 interposed between the ring member 11 and the carrier permits adjustment of the electromagnets 10 and pole pieces 5 with respect to diaphragm 1. without setting up interfering noises and rattles in the sound rcproducer.

The enlarged cross-sectional view of the diaphragm, as illustrated in Fig. 3 sets forth the invention more clearly showing the perforations 2 closed by the insulating compound 14 having a density less than the magnetic material of the diaphragm and substantially inert to the efiects of eddy currents. The insulating compound 14 does not impair the flexible properties of the sound reproducing diaphragm and yet prevents interference between sound waves from the rear of the diaphragm in the area designated at 1 5 in Fig. 2 from interfering with sound waves in front of the diaphragm in the area designated at 16 in Fig. 2. One of the inherent defects in many constructions of loud speakers is the reaction between the difi'ering phase of sound waves emanating from opposite sides of the diaphragm and my construction avoids the setting up of this undesired disturbance.

Fig. 4 shows the results of investigations of sound reproducing diaphragm and a comparison of the results obtainable with diaphragms of the usual construction and the results obtainable with the dia hra of m to show relative sound intensity with respect to frequency range. obtainable from an electromagnetic sound reproducer employing sound reproducing diaphragrns of differing construction; that is a solid diaphragm of y the usual construction, a diaphragm perforated in accordance with the construction of diaphragm described herein, but Without the material 14 closing the perforations and a diaphragm constructed in accordance with the invention herein having perforations entirely closed by the sound insulating material 14. Curve A shows the results obtainable with a standard solid construction diaphra m. Curve C illustrates the results obtainaile with a diaphragn'i which is perforated as represented at 2 in Fig. 1, but without the filling of sound insulating matcrial 14 in the perforations. The curve C shows the decided decrease in sound intensity which is obtainable when the diaphragm is perforated. Curve B, however, shows'the marked improvement which is obtainable by means of the diaphragm construction ofgreater sound intensity than is possible in diaphragms of solid construction.

The diaphragm construction of this in" vention is the result of an extended series of sound investigations and the practical re sults obtainable have established the real merit in this type of diaphragm. e low notes which are normally sacrificed with the standard diaphragm construction are faithfully reproduced by the diaphragm construc tion of my invention.

I desire that it be understood that various kinds of sound insulating material may be employed to fill the perforations 2 in the sound reproducing diaphragm and that no limitations upon the invention are intended other than those imposed by the scope of the appended claims.

What I claim and desire to secure by Letters Patent of the United States is as follows:

1. A sound reproducing magnetic. diaphragm, comprising an outer peripheral solid portion arranged to be supported adjacent an electromagnet, a central solid portion, and an intermediate portion perforated in concentric circles along radial lines of said diaphragm with the perforations of one circle alternately positioned with respect to the perforations of an adjacent circle for y increasing the flexibility of said diaphragm, improved construction. The 0 art is plotted and sound insulating non-magnetic material filled within said perforations for preventing reaction between sound waves emanating from the opposite sides of said diaphragm whereby a relatively wide path for the threading of magnetic lines through the center of said diaphragm is provided independent of the flexibility of said diaphragm.

2. A sound reproducing magnetic diaphragm positioned adjacent a set of electromagncts, said sound reproducing diaphragm having an outer solid peripheral edge arranged to be supported from the edge thereof and a solid central portion arranged to be positioned in immediate alignment with the set of clcctromagnets. and an intermediate perforated portion between said cen tral portion and said outer peripheral edge for increasing the flexibility of said diaphragm, the perforations of said intermediate portion being arranged in concentric circular rows, with one circular row of pernos forations offset with respect to the adjacent c rcular row of perforations. said perforations belng filled with non-magnetic material having a density less than the density of the diaphragm and being substantially inert to the effects of eddy currents whereby a relatively wide path for the threading of magnetic lines through said diaphragm is provided independent of the flexibility of said diaphragm and sound waves emanating from one side of said diaphragm are prevented from reacting with sound waves emanating from the opposite side of said 10 diaphragm.

' In testimony whereof I aflix my signature.

CECIL E. BRIGHAM. 

